Prion diseases are neurodegenerative diseases of humans and animals, which are invariably fatal and lead to death within a year after the onset of clinical symptoms. As with most other neurodegenerative diseases, no effective therapy is known. Treatment of patients with sporadic (s) Creutzfeldt-Jakob disease (CJD), the most common human prion disease, employing quinacrine will be studied. CJD patients will initially receive a racemic mixture of quinacrine. Quinacrine has been shown to inhibit prion formation in cultured ScN2a cells at submicromolar concentrations. Additionally, experimental prion disease in mice will be treated with quinacrine. In studies with ScN2a cells, the (S)-quinacrine isomer was 2 to 3 times more potent with respect to inhibiting prion formation than (R)-quinacrine; these isomers will be compared to the racemic mixture in mice. Concurrently, murine models will be used to evaluate treatment of prion disease with new drugs produced through empirical and rational drug design. The empirical drug program will utilize a combinatorial chemistry approach with quinacrine as the lead compound. Quinacrine will be modified and tested in the ScN2a cell culture system. We plan to test about 2000 new quinacrine analogs per year. Only compounds that are 10 times more potent than quinacrine with respect to antiprion activity will be evaluated in mice. Initially, these new antiprion compounds will be screened for toxicity. Compounds that are determined to be sufficiently nontoxic will then be tested for their ability to block prion synthesis in transgenic (Tg) mice. Besides empirical drug discovery, we plan to expand a rational drug design program along two lines of investigation. Attempts will be made to increase the potency of quinacrine by further modifying the aliphatic side chain. Recent studies have shown that bis-quinacrine analogs are more potent than quinacrine by a factor of ten. We also plan to dissect the mode of quinacrine action through studies of PrP trafficking in cultured cells. A second line of rational drug design involves modifying compound 60, which was found by mimicking dominant negative inhibition of prion synthesis. In order to understand dominant negative inhibition of prion synthesis, the structures of dominant negative PrPs will be determined using NMR spectroscopy. The information obtained from these dominant negatives should facilitate improvements in the design of existing drugs or lead to the production of new drugs.